The lithiation of monosubstituted ferrocenes bearing chiral or achiral directing groups1,2 is a key method for the preparation of planar chiral reagents with applications in catalysis3 and materials science.4 Carbon-based directing groups that have been developed for this purpose include (dialkylaminomethyl)ferrocenes5 (e.g., 1), oxazolines6 (2), acetals7 (3), hydrazones5 (4), and carboxamides9 (5), which impart planar chirality by diastereoselective or enantioselective deprotonation (Scheme 1).1,2,10 The most commonly employed heteroatom-based directing groups are chiral sulfoxides 6 (R=p-Tol, t-Bu)11 and related sulfoximines,12 derivatives of which have been applied in asymmetric synthesis.3a More recently, nonstereoselective lithiation of ferrocenyl benzimidazoles (7) has also been reported.13

A rekindling of interest in aminoferrocenes in recent years has resulted in planar chiral ligands such as aminosulfoxide 8 (Scheme 2), which is prepared by “E+” electrophile quench of the 2-lithio derivative of sulfoxide 6.14 In contrast, ferrocenyl N-heterocyclic carbenes15 (9) and aminophosphines16 (10) have been prepared by more circuitous routes involving Curtius rearrangement of ferrocene-2-carboxylic acids derived from 3 and 1.
